1. Field of the Invention
The invention relates to a cleaning apparatus, particularly to a cleaning apparatus removing an organic material for an organic EL element attaching to a mask made of a thin metal film in a process of vapor-depositing the organic material.
2. Description of the Related Art
In recent years, an organic electroluminescent (hereafter, referred to as EL) display device with an organic EL element is receiving attention as a display device substituting for a CRT and an LCD. For example, research and development are being pursued for the organic EL display device having a driving thin film transistor (hereafter, referred to as a driving TFT) for driving the organic EL element.
The organic EL element has a structure laminated with an anode made of ITO, a hole transport layer made of a first hole transport layer made of MTDATA (4,4-bis(3-methylphenylphenylamino)biphenyl) and a second hole transport layer made of TPD (4,4,4-tris(3-methylphenylphenylamino)triphenylanine), an emissive layer made of Bebq2 (bis(10-hydroxybenzo[h]quinolinato)beryllium) containing a quinacridone derivative, an electron transport layer made of Bebq2, and a cathode made of aluminum alloy and so on, in this order.
In such an organic EL element, light is emitted by flowing a current through the driving TFT for driving the organic EL element. That is, holes injected from the anode and electrons injected from the cathode are recombined in the emissive layer and excitons are generated by exciting organic molecules forming the emissive layer. Light is emitted from the emissive layer in a process of radiation of the excitons and then released outside after going through the transparent anode to the insulation substrate made of a glass substrate or the like, thereby completing light-emission.
Organic materials used for forming the hole transport layer, the emissive layer, and the electron transport layer among the layers of this organic EL element have low resistance to solvents and moistures. Therefore, a photolithography can not be used in a semiconductor process. Therefore, pattern formation of the hole transport layer, the emissive layer, the electron transport layer, and the cathode of the organic EL element has been made by selectively vapor-depositing the organic material on the insulation substrate having the driving TFT by a vapor-deposition method using a mask (a so-called shadow mask) made of, for example, a thin metal film.
An example of such a mask used when the organic material is vapor-deposited is shown in FIGS. 15 to 17. FIG. 15 is a top view of a conventional mask for forming an organic EL element. FIG. 16 shows a cross-sectional view along line X-X of FIG. 15, and FIG. 17 shows a cross-sectional view along line Y-Y of FIG. 15. As shown in FIGS. 15 to 17, a mask 10 is made of a thin metal film such as nickel (Ni) and iron (Fe) with a plurality of fine holes 11 of several micrometers by several micrometers. The organic material is selectively vapor-deposited on the insulation substrate through these holes 11.
The mask 10 made of the thin metal film is fixed to a metal frame 12 made of, for example, nickel (Ni) and iron (Fe), and an edge of the mask 10 is supported by the metal frame 12. An edge of the metal frame 12 is formed with a plurality of lock portions 13 for holding the metal frame 12. Hereafter, the mask 10 fixed to the metal frame 12 will be collectively called the “mask 10.”
The relevant technology is disclosed in Japanese Patent Application No. 2004-103269.
When the organic EL element has emissive layers of three primary colors of red, green, and blue for color display, generally, the process of vapor-depositing the organic material is performed by repeatedly using the mask for each of the colors. Therefore, as the number of repeated vapor-deposition processes increases more, more organic materials are attached and laminated on a surface of the mask 10. That is, as shown in FIG. 18 showing a cross-sectional view of the mask vapor-deposited with the organic material, the organic material 1 is attached not only to the surface of the mask 10 but also to edges of the holes 11 to form overhangs 1a almost blocking the holes 11 which the organic material 1 passes through.
In this manner, since the holes 11 of the mask 10 are narrowed by the overhangs made of the organic material, there is a problem that accuracy in vapor-depositing the organic material on the insulation substrate lowers.
For solving this problem, there is a method of discarding a used mask and using an unused mask in each vapor-deposition process without reusing the same mask. However, in this method, there is a problem that the cost increases because the masks used for vapor-depositing the organic material for an organic EL element are expensive.